2,3,3,3-Tetrafluoropropene represented by the formula CF3CF═CH2 (HFO-1234yf) is a compound that is useful as a refrigerant.
Patent Literature (PTL) 1 listed below, for example, dFiscloses a process for preparing HFO-1234yf, wherein a compound represented by CX3CF2CH3 (X is a halogen atom) is contacted with hydrogen fluoride in the presence of chromium oxyfluoride at a molar ratio of hydrogen fluoride to the starting material of 2-40 mol to 1 mol. In Patent Literature 1, however, CCl3CF2CH3 (HCFC-242cb) is the only compound specifically used as the starting material, in which case hydrogen fluoride is used in large excess, i.e., in an amount of 18 mol per mol of the starting material, resulting in poor efficiency.
Non-Patent Literature (NPL) 1 proposes a reaction route that includes the production of CF3CFClCH3 (HCFC-244bb) by 1,2-rearrangement of Cl and F in CF2ClCF2CH3 (HCFC-244 cc), followed by the elimination of HCl, thereby producing HFO-1234yf. As a result of the test conducted by the present inventors, however, the reaction via this reaction route did not proceed. Therefore, HFO-1234yf cannot be obtained by the process disclosed in Non-Patent Literature 1.
As another preparation process, Non-Patent Literature 2 discloses a single-step process wherein CF3CF2CH2X (X═Cl or I) is reacted with zinc (Zn) in ethanol. This process, however, is not suitable for industrial-scale production, since zinc is expensive, and large amounts of wastes are produced. Patent Literature 2 listed below discloses a process that involves the synthesis of CF3CF═CCl2 (HFC-1214ya) by dehydrofluorination of CF3CF2CHCl2 (HCFC-225ca), and reduction of the HFC-1214ya with hydrogen in a gas phase in the presence of a palladium catalyst supported on a carrier such as alumina, fluorinated alumina, aluminum fluoride, or a mixture thereof, thereby obtaining a mixture containing at least 50% of HFO-1234yf. This process also, however, does not provide a satisfactory yield, and requires further improvement.
Other processes for preparing HFO-1234yf that have been reported include a process wherein chloromethyl tetrafluoropropanoate is reacted with an amine (Patent Literature 3); a process that involves the thermal decomposition of
1-trifluoromethyl-1,2,2-trifluorocyclobutane (Patent Literature 4); a process wherein chlorotrifluoroethylene (CClF═CF2) is reacted with methyl fluoride (CH3F) in the presence of a Lewis acid such as SbF5 (Patent Literature 5); and
a process that involves the thermal decomposition of tetrafluoroethylene (CF2═CF2) and chloromethane (CH3Cl) (Patent Literature 6). Further, Non-Patent Literatures 3 and 4 listed below also disclose processes for preparing HFO-1234yf.
These processes, however, are not considered to be effective for industrial purposes since the starting materials are difficult to produce and are not easily obtained, the reaction conditions are severe, the reaction reagents are expensive, the yield is low, etc. Thus, there is a need for an economically suitable process for easily producing HFO-1234yf.